Generally, in the conventional open-end spinning machine shown in FIG. 1, a bundle of fibers, that is, a sliver 3 supplied through an inlet 2 of a spinning unit 1 is transported to a combing roller 6 by means of a feed roller 4 in cooperation with a presser 5 which presses the sliver 3 onto the feed roller 4. Then, the sliver 3 is opened into individual fibers by the combing roller 6 and, at the same time, impurities 7, such as leafage, trash and the like, are expelled through an outlet 8. The opened fibers are transported to a spinning chamber 10 of a high-speed rotor 9 through a fiber supply duct 11 by an airstream Y created by negative pressure in the spinning chamber 10 of the rotor 9 rotating at high speed. The fibers thus transported into the spinning chamber 10 reach an inner wall 9a of the rotor 9 through a circular stream created in the spinning chamber 10 by the working of the rotor 9 rotating at high speed. Then the fibers slide toward a fiber-collecting portion 13 which is the greatest inner-diameter portion. In the fiber-collecting portion 13, the fibers are collected and twisted in the shape of a ribbon. The fiber ribbon is drawn out in the form of a yarn 31 through a yarn guide hole 14 which is provided in the center of a closing member 20.
The rotor 9 has the spinning chamber 10 closed by the inner wall 9a and a bottom portion 9b. An open end of the spinning chamber 10 opposite the bottom portion 9b is substantially closed by the closing member (boss portion) 20 formed by part of the frame of the spinning unit 1. The closing member 20 projects into the spinning chamber 10 of the rotor as a boss portion in which an opening portion 111 of the fiber supply duct 11 and a yarn guide opening portion 141 of the yarn guide hole 14 are provided, respectively. Here, in order to draw the fibers into the spinning chamber 10 through the fiber supply duct 11, it is necessary to provide negative pressure in the spinning chamber 10 to form an airstream toward the spinning chamber 10 from the fiber supply duct 11.
There are three kinds of systems for airstream formation. A first system is of the force exhaustion type in which the air in the spinning chamber 10 is sucked out from an upper-side opening end of the rotor by a suction means (not shown) connected to an exhaust port 16 provided in a casing 15 covering the rotor 9. A second system is of the self-exhaustion type in which the air in the spinning chamber 10 is expelled through a plurality of exhaust ports 9c provided radially in the bottom portion 9b of the rotor 9 by centrifugal force imparted by the rotor 9. A third system is of the self-and-forced exhaustion type in which the forced exhaustion and the self-exhaustion are used in combination.
On the other hand, a channel system and a separator system are now used as means for supplying fibers into the spinning chamber 10. The channel system is of the type in which the fibers are supplied into the spinning chamber 10 through the opening portion 111 provided on a side wall of the boss portion 20 so that the opening portion 111 directly faces the inner wall 9a of the rotor as shown in FIG. 1. The separator system is of the type in which the fibers are supplied into the spinning chamber 10 through the opening portion 111 provided on an end surface of a semicircular slit 201 (FIG. 20 and FIG. 21) formed in a side wall of the boss portion 20 as shown in FIGS. 11 through 13.
In those systems of open-end spinning machines, the high-speed revolution of the rotor (about 50,000 to 100,000 rpm) has been progressed. With the progress of the revolution speed of the rotor, the diameter of the rotor has decreased. The necessity of reducing the diameter of the rotor with the progress of the revolution speed of the rotor is due to the following reason.
As shown in FIG. 23, the spinning tension F applied to the yarn is represented by the equation: EQU F=(1/2).times..rho.(D/2).sup.2 .omega..sup.2 e.sup..mu.(.theta.1+.theta.2)
where .rho. represents the linear density (kg/m) of the yarn, D represents the greatest inner-diameter (m) of the rotor, .omega. represents the angular velocity (rad/s) of the rotor, .mu. represents the coefficient of frictional between the yarn and the guide, and .theta..sub.1 and .theta..sub.2 represent the contact angles (rad) between the yarn and the guide when the yarn is drawn out.
Let the revolution speed of the rotor now be increased, then the tension F applied to the yarn increases in proportion to a square of the revolution speed of the rotor. When the tension F increases, end breakage occurs during spinning or the elasticity of the yarn thus produced is lost. The large tension F has an adverse influence on the handling of the spinning machine and the quality of the yarn. The diameter of the rotor must be reduced in order to attain high-speed revolution of the rotor.
Although the diameter of the rotor has been reduced with the progress of the high-speed revolution of the rotor, over-reduction of the diameter of the rotor to attain higher-speed revolution of the rotor induces yarn evenness and lowering of yarn strength so as to deteriorate the quality of the yarn.
Investigating the cause, the yarn guide passage (yarn guide hole) in the prior art is arranged in the center of the end surface of the boss portion in the conventional system. Therefore, it is necessary to arrange the fiber supply duct (channel passage) 11 to avert the yarn guide hole 14. Because the diameter of the boss portion 20 decreases as the diameter of the rotor decreases, the size of the fiber supply duct 11 is limited by the size of the boss portion 20. In short, the sectional area of the fiber supply duct must be reduced as the diameter of the rotor decreases as shown in FIG. 24. The same tendency exists both in the case of a channel system and in the case of a separator system. Accordingly, the following description is made only for the case of a channel system.
When the sectional area of the channel passage decreases as the diameter of the rotor decreases, air resistance increases, so that the air flow from the channel passage decreases. Consequently, the fibers flying within the channel cannot be placed on the airstream well so that the fibers are bent by collision with the wall of the channel to thereby shorten effective fiber length or the fibers during flying are entangled with each other to thereby produce yarn evenness.